This paper proposes an object-based framework for the development of heterogeneous, composite systems. Such systems require the use of multiple notations and development strategies to describe multiple developer perspectives. The framework employs coarse-grain objects, called ViewPoints, that represent "agents" having "rolesin" and "views-of" a problem domain. These ViewPoints are loosely coupled, locally managed encapsulations, integrated via inter-ViewPoint consistency relations and transformations.Tool integration is treated as a special case of method integration, and is demonstrated by The√iewer -a prototype support environment presented in this paper. The√iewer supports the proposed framework, and illustrates how ViewPoints may be used for method design, description, integration and use. Developed in Objectworks/Smalltalk, it maps the object-based framework onto an object-oriented implementation. The top level architecture and implementation of The√iewer is also briefly presented.